Fabrication of semiconductor device such as logic and memory device may include processing wafer through various semiconductor processing tools. As feature sizes continuously shrink, for example, from 45 nm to 32 nm, processing parameters such as focus accuracy become critical for lithography and metrology tools. The image focusing in an e-beam inspection practice is mainly through the objective lens. Many auxiliary lens have been adopted to determine the position of the specimen surface to fine tune the image focus. The most popular method adopted in e-beam inspection tool to assist system focusing is laser related auxiliary focus. However, the detecting accuracy of laser is limited within the range of 0.5 μm to 0.01 μm due to wafer surface pattern diffraction. Other conventional accuracy methods take a series of e-beam images that not only take a long time but also may contaminate the processing wafer.
Therefore, an improved system and method for fast respond lens and high speed focusing check is desired. The present invention addresses such a need.